1. Field of the Invention
This invention relates to improvements in a fuel injection valve drive system for use in an internal combustion engine having at least one solenoid operated fuel injection valve.
2. Description of the Prior Art
Fuel injection valve drive systems have been used in spark ignition type internal combustion engines having a plurality of fuel injection valves disposed at the intake ports of the respective cylinders or a single fuel injection valve disposed at the entrance of the intake manifold. Such a fuel injection valve drive system is adapted to provide, in synchronism with rotation of the engine, a drive pulse signal having a pulse width corresponding to the amount of air introduced to the engine, to operate the fuel injection valve(s). The fuel injection valve(s) is opened each time a pulse is applied thereto and remains open throughout the duration of the pulse to discharge a controlled amount of fuel therethrough so as to provide a predetermined air-fuel ratio. Particularly in single point fuel injection systems where a single fuel injection valve is provided at the entrance of the intake manifold, the fuel injection valve usually has a relatively large opening size to allow injection of fuel in amounts required for all of the cylinders over the broad fuel range from idling to high load conditions. Further, the period of opening of the fuel injection valve varies over the broad range of fuel demand and can be as short as about 2 msec or less during idling. Since single point injection valves utilize a winding of large impedance, it is very difficult to control the fuel injection valve without undue fluctuations in the amount of fuel injected though the fuel injection valve. As a result engine operation and increased undesirable exhaust emissions are experienced when a small amount of fuel is required, such as during idling.